Case Study:TV Booting and Flashing Fault Analysis/TCL LED L24E09

Fri Dec 21 11:14:39 CST 2018

Case Study:TV Booting and Flashing Fault  Analysis/TCL LED L24E09

Fault: The boot screen TCL logo has just been displayed, and then automatically shuts down.

Overhaul process: Check the power output 12V, 5V are very normal and start the second boot. Only see the boot level is normal immediately and immediately turn off the level. The BRT signal voltage becomes 0 right away.

Maintenance ideas: The machine is a three-board type. The main board, the power board, and the backlight board are independent small boards. When the power is turned on, the power has a low-level signal (the motherboard is low-level boot), and the momentary protection is turned off. After the fault occurs, check that all the supply voltages are normal, and the fault can be determined as a backlight or a motherboard.

According to experience, simulate a boot signal to narrow the range. The conventional method is to short-circuit the power pin to ground (low level), and add +5V to the BRT pin. However, the TV will still not start and the screen will not respond. Disconnect the BRT pin +5V voltage, the motherboard still can't boot, plug in the antenna and there is no sound, strange! The voltage of each group is normal, the TV will start up instantly, and there is no sound after the startup. Is the motherboard system unable to boot?

With the principle of maintenace, call the after-sales service department of the city to ask if there is a backlight. After-sales friends asked me to take the whole machine, and by the way, help me judge.

Come to the service department, try to change the backlight board, boot, sound and light appear. Trouble shooting!

 

 

Internal technical analysis:

The L24E09 has two main board control modes.The first one is the low level boot type. Due to poor backlight component (suspicion is short circuit of high voltage transformer), the motherboard CPU detects the circuit overcurrent, and the system implements protection shutdown. At this time, even if you simulate the boot condition, the system will not start. so when the antenna is plugged in, there is no sound. Please be careful!

The second type is a high level booting motherboard. When the system detects overcurrent, it only turns off the BRT signal, and the motherboard can work as well. At this time, although the screen is not bright, plugging in the antenna can listen to the radio sound. This kind of circuit is easy to judge. If the above situation occurs, there are two reasons:the backlight is bad, and the screen is bad. On the contrary, it can be judged that the motherboard is faulty.

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